Java框架SSM：mybatis之二 一对多的关系

mybatis一对一的关系

接下来是一对多的关系！

son

sid	sname
1	张三
2	李四

dog

did	dname	sid
1	泰迪	1
2	二哈	2
3	藏獒	1

可以看出张三有两只狗，分别是泰迪和藏獒。

而李四只有二哈一只狗。

接下来，上代码。

package com.hc.entity;

import java.util.List;

public class Son {
    private int sonId;
    private String sonName;
    private List<Dog> dogs;

    public Son() {
    }

    public Son(String sonName) {
        this.sonName = sonName;
    }

    public int getSonId() {
        return sonId;
    }

    public void setSonId(int sonId) {
        this.sonId = sonId;
    }

    public String getSonName() {
        return sonName;
    }

    public void setSonName(String sonName) {
        this.sonName = sonName;
    }

    public List<Dog> getDogs() {
        return dogs;
    }

    public void setDogs(List<Dog> dogs) {
        this.dogs = dogs;
    }
}

这是son的表。

son有一个属性类型为List<Dog>;

private List<Dog> dogs;

这是为了能够承装某son多条狗。

package com.hc.entity;

public class Dog {
    private int dogId;
    private String dogName;
    private Son son;

    public Dog() {
    }

    public Dog(String dogName) {
        this.dogName = dogName;
    }

    public int getDogId() {
        return dogId;
    }

    public void setDogId(int dogId) {
        this.dogId = dogId;
    }

    public String getDogName() {
        return dogName;
    }

    public void setDogName(String dogName) {
        this.dogName = dogName;
    }

    public Son getSon() {
        return son;
    }

    public void setSon(Son son) {
        this.son = son;
    }
}

这是dog，dog有一个属性是主人son。

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hc.dao.UserDao">


    <resultMap id="SonDog" type="Son">
        <id property="sonId" column="sonId"></id>
        <result property="sonName" column="sonName"></result>

        <collection property="dogs" ofType="Dog" select="selDog" column="sonId">
            <id property="dogId" column="dogId"></id>
            <result property="dogName" column="dogName"></result>
        </collection>


    </resultMap>


    <select id="allSon" resultMap="SonDog">
        select * from son
    </select>

    <select id="selDog" resultType="Dog" parameterType="int">
        select * from dog where sonId=#{sonId}
    </select>

</mapper>

这是关系的配置，Son.xml。

collection：相当于son对象中的List<Dog>

    <collection property="dogs" ofType="Dog" select="selDog" column="sonId">
            <id property="dogId" column="dogId"></id>
            <result property="dogName" column="dogName"></result>
        </collection>

collection select：在collection里调用了一个子查询selDog

<collection property="dogs" ofType="Dog" select="selDog" column="sonId">

非常nice。

package com.hc.dao;

import com.hc.entity.Son;
import com.hc.entity.User;
import java.util.List;

public interface UserDao {
    public List<User> allUser();
    public List<Son> allSon();
}

这是dao接口。

package com.hc.test;

import com.hc.dao.UserDao;
import com.hc.entity.Dog;
import com.hc.entity.Son;
import com.hc.entity.User;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.util.List;

public class First {

    private SqlSession session;
    private UserDao userDao;

    @Before
    public void before(){
        SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(getClass().getClassLoader().getResourceAsStream("myBatis-config.xml"));
        session = factory.openSession();
        userDao = session.getMapper(UserDao.class);
    }

    @Test
    public void testallSon(){

        List<Son> sons= userDao.allSon();
        for (Son son : sons) {
            System.out.println(son.getSonId()+"\t"+son.getSonName());
            for (Dog dog : son.getDogs()) {
                System.out.println(dog.getDogId()+"\t"+dog.getDogName());
            }
            System.out.println("\n");
        }
    }


    @Test
    public void testallUser(){
        List<User> users= userDao.allUser();
        for (User user : users) {
            System.out.println(user.getUserId()+"\t"+user.getUserName());
            System.out.println(user.getCard().getCardId()+"\t"+user.getCard().getCardNum());
            System.out.println("\n");
        }
    }

    @After
    public void after(){
        session.commit();
        session.close();
    }
}

单元测试，运行testallSon

@Test
    public void testallSon(){

        List<Son> sons= userDao.allSon();
        for (Son son : sons) {
            System.out.println(son.getSonId()+"\t"+son.getSonName());
            for (Dog dog : son.getDogs()) {
                System.out.println(dog.getDogId()+"\t"+dog.getDogName());
            }
            System.out.println("\n");
        }
    }

则可以获取到某son的多条狗。

非常好用！nice！